Membrane switches, also known as tactile or pressure sensitive switches, typically include a pair of resilient laminae. Such laminae are frequently made from a polyester material. Each lamina has a silver conductive ink circuit screened on one side thereof, and the sides upon which the circuits are printed are facing proximately one another. The laminae are arranged so that the circuits will be superimposed on one another when the laminae are in engagement. A spacer, which can also be manufactured from a polyester material, is positioned intermediate the laminae and, in many instances, has a window cut out at the location of the silver conductive ink circuits in order to enable the circuits to be brought into engagement. The spacer can be secured to the laminae by a pressure sensitive adhesive.
Depending upon the thickness of the spacer, the size of the window can be varied while yet maintaining the laminae in a normally non-engaged relative positioning. When pressure is applied to the laminae, however, urging them together, the circuits screened onto the laminae are brought into engagement to close a switch and effect a function. The function which will be effected depends upon the application to which the switch is being put. Such switches can be used in keyboards for computers, controls for microwave ovens, and dispensing switches for vending machines. In this latter specific application, it is frequently desirable to back light the switch in order to make the display of the selection keys more attractive. When the switch is manufactured as known in the prior art, the silver conductive ink circuits screen printed onto the laminae preclude the usage of back lighting to illustrate the particular function. Since such traces are opaque, the indicia illustrated on the switch become distorted in view of the ink circuits applied to the laminae.
The invention of the present application is a membrane switch which solves the problems of the prior art as discussed above. It can be used with a back lighting method of representing indicia of the function to be effected without any distortion of the indicia being caused by the silver conductive ink circuit.